Hi,
I have a 30 yr. old house with the usual electrical system of circuit breakers. There is one breaker which is a GFIC type complete with a test button. This circuit runs into the outlet in the bathroom and an outdoor outlet. We had a Christmas light set up using the outside outlet when a lot of rain soaked the lights out front. I turned the lights on and they went on for less than a minute then all went out. I checked the circuit breaker and it had tripped. I reset it but nothing happened. I double checked the outlet in the bathroom and it doesn't work either. The test button on the breaker doesn't reset despite switching the breaker back and forth. Any advice out there?

unplug everything from the protected circuit, especially the offending drenched xmas lights. Turn off anything switch controlled which is hardwired, like bathroom lights. don't overlook anything, such as a plugged in night light or an electrified medicine cabinet (combo night fixture and/or receptacle). protect the outside receptacle. let it dry out keep the circuit OFF until you have assured this is completed.

Unplug anything that is currently connected to that circuit .
See if the breaker will reset . Is the outside receptacle dry ?
Could be a bad breaker .

Do you know how the circuit runs ? Does it go to the bathroom first ( typical ) and then continue to the outside recpt. ?

If you can determine that , you might consider replacing the GFCI breaker with a conventional type , and using a GFCI receptacle in the bathroom to protect it and the outside recpt .
Make sure the recpt. is wired correctly as to Line/Load , and obviously make sure that your local code allows this .

Unplug anything that is currently connected to that circuit .
See if the breaker will reset . Is the outside receptacle dry ?
Could be a bad breaker .

Do you know how the circuit runs ? Does it go to the bathroom first ( typical ) and then continue to the outside recpt. ?

If you can determine that , you might consider replacing the GFCI breaker with a conventional type , and using a GFCI receptacle in the bathroom to protect it and the outside recpt .
Make sure the recpt. is wired correctly as to Line/Load , and obviously make sure that your local code allows this .

It sounds to me water is still somewhere in the circuit.
In regards to the wiring many a house in Pa. were wired that exact same way. What a headache that creates for homeowners & sparkys alike.
Thankfully it no longer an allowable practice.